This invention relates to a heat exchanging device of lubrication oil for exchanging heat of lubrication oil which circulates in a transmission of a vehicle.
In conventional arts, some transmissions of a vehicle have gear mechanism and clutch (friction engaging device) for switching an engagement/disengagement power transmission between a driving source and a transmission mechanism disposed in a same chamber (in a same case). In the transmission, the above-described clutch and gear mechanism are lubricated and cooled by the same lubrication oil (ATF: Automatic Transmission Fluid). On the other hand, some transmissions have clutch and gear mechanism respectively disposed in mutually different chambers (in different cases) and different kinds of lubrication oils respectively used for lubricating the clutch and for lubricating and cooling the gear (Japanese Unexamined Patent Application Publication No. 2003-14090). In these transmissions, using an exclusive lubrication oil for the clutch enhances lubricating and cooling effect on the clutch.
In general, a big capacity of the clutch is needed to transmit a large torque when a vehicle is required to have a high level of power performance. Therefore, the clutch often produces a problem of increasing generation heat or durability and the like. On the other hand, when the clutch is provided with a conventional air cooling system or water cooling system described above as a cooling system for lubrication oil, the problems described below can be occurred.
A cooling air taken into an air cooler is low while the vehicle is running at a low speed when using an air-cooled cooling system as a cooling system for lubrication oil. Thereby, a cooling effect for lubrication oil is remarkably lowered. In addition, a vehicle body needs to be provided with a large aperture to introduce enough cooling air into the air cooler. This can affect a design of the vehicle body. Furthermore, the air cooler needs to be disposed on a front part of the vehicle to be provided with a big aperture to introduce the cooling air. Therefore, when a transmission is on the rear part of the vehicle body, a pipeline for oil needs to be arranged from the rear part up to the front part of the vehicle body. Thereby the pipeline for lubrication oil becomes long. Thus, oil resistance in the pipeline increases, and a pressure of lubrication oil needs to be raised in order to make lubrication oil circulate with a large flow rate. In addition, when the pipeline for lubrication oil becomes long, the weight of the vehicle body increases and the layout of the piping becomes complicated.
On the other hand, when using the water cooling system as a cooling system for lubrication oil, the lubrication oil and other components (for example, an engine) are cooled by the same cooling water of the cooling system. Therefore, enough cooling of lubrication oil can be prevented. Also, when the temperature of the cooling water rises, there is a risk that the water temperature cannot meet a required temperature for cooling the engine and other components. Furthermore, the flow rate of the cooling water (pump capacity) is predetermined and there is a certain temperature condition that lubrication oil can be possibly prevented from being cooled enough due to the shortage of the flow rate of the cooling water.
On the other hand, when the vehicle is provided with the air cooler as a cooling means for lubrication oil for lubricating the clutch and the gear and the likes of the transmission, the radiation heat in the air cooler becomes excessive in quantity, thereby the temperature of lubrication oil is possibly excessively lowered. This can increase friction resistance (friction) of the clutch and the gear.